You can drag and drop bookmarks and bookmark folders from Opera to Chrome directly, but you cannot do the reverse. So you could drag your bookmarks to Chrome and then save them to an HTML file from Chrome.

There should be a way to backup bookmarks (export, which opera 12 had, extension .adr).

You can backup any data of any program on your computer without needing to rely on the own programs to do it.

In the case of Opera, just backup its profile folder.

What I mean is that all major browsers (including the infamous IE) have an option to export bookmarks (to save them or to import to other browsers) including opera 12, so, the not so new now opera should have this option. Just saying.